摘要:

AbstractThe conformational and enthalpic changes that occur in poly(vinyl chloride) (PVC) glasses that have been vitrified from the melt under pressure have been examined by Fourier transform infrared spectroscopy and quantitative differential scanning calorimetry. It is shown that these pressures freeze in the high energy states that are characteristic of the vitrification temperature and increase the apparent glass transition temperature of the polymer. In addition, pressures in excess of the vitrification pressure, cause intermolecular effects that can be relaxed out belowTg. Both of these processes create characteristic endothermic and exothermic changes in the apparent heat capacity of the glass that appear over a period of time and are sensitive functions of the glass formation processes as well as the subsequent annealing history. The endothermic events are interpreted as the stress perturbed volumetric relaxation process white the exotherms are associated withh the release of the frozen in stresses.

ISSN:0032-3888    

DOI:10.1002/pen.760211802

出版商:Society of Plastics Engineers, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractA new model for the curing kinetics of diurethane crosslinked natural rubber is elaborated. On the basis of rheometric data, calculation of rate constants of both formation and degradation of the following bond types: urea‐urea, urethane‐urethane, and urea‐urethane, was enabled and thermal activation energies of these processes were determined. Activation energy values for formation of the bonds above are: 61.5 kJ/ mole, 187.6 kJ/mole, and 28.9 kJ/mole, respectively. For degradation, activation energies are: 293.9 kJ/mole, 195.5 kJ/mole, and 163.3 kJ/mole, respectively. An algorithm for carrying out of these calculations on a computer was deve

ISSN:0032-3888    

DOI:10.1002/pen.760211803

出版商:Society of Plastics Engineers, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractThe residence time distribution in an industrial single screw extruder was investigated experimentally in the case of melt and plasticating extrusion. The investigations performed proved that the extrusion parameters influence strongly the residence time distribution in the extruder. It was found that the resistance to flow through the die‐head of the extruder is very important from this point of view, as well as other parameters like rotational speed of the screw and the screw channel depth. Variation of these parameters can change the residence time distribution over a broad range between the extreme idealized cases of plug flow and flow with perfect mixing. In order to obtain quantitative dependences three moduli were used and a correlation equation was obtained. This equation enables an estimation of residence time distribution on the basis of experimental characteristics of the extruder and the actual extrusion parameter

ISSN:0032-3888    

DOI:10.1002/pen.760211804

出版商:Society of Plastics Engineers, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractWhen a thermoplastic specimen is tested in flexural fatigue, the viscoelastic behavior of the material combines with the heat dissipation mechanism to generate an equilibrium temperature distribution. In order to locate the starting point of an eventual fatigue crack in the most stressed section of a particular geometry, it is important to know where the temperature reaches its maximum value. A first mathematical model has been proposed to evaluate the temperature distribution across the thickness of the specimen. Solutions have been obtained analytically and by a finite difference method. A comparison of the solutions enabled us to optimize the mesh size, the relaxation factor and the convergence criterion in the finite difference scheme in order to get results within a chosen accuracy. Preliminary test results are given and compared with the theoretical temperature distribution for two thermoplastics, nylon 66 and acetal homopolymer.

ISSN:0032-3888    

DOI:10.1002/pen.760211805

出版商:Society of Plastics Engineers, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractReaction injection molded (RIM) polyurethanes, especially reinforced RIM polyurethanes, are promising candidates to replace metal exterior body panels on automobiles. One of the most important performance properties which these RIM parts must possess is thermal dimensional stability. Thermal dimensional stability is defined as the ability of a part to withstand distortion or change in size during thermal cycles. This property is important for two reasons. First, during paint operations parts are exposed to high paint bake temperatures. Second, parts may be exposed to relatively high temperatures in use. Thermal dimensional stability is mostly controlled by formulation and post‐treatment. Formulation can change the structure of the polymer leading to different thermal properties. Posttreatment such as annealing can change (a) the degree of hard segment phase order, (b) the degree of phase separation and (c) the relative continuity of the phases. Experimental evidence is given to support all these factor

ISSN:0032-3888    

DOI:10.1002/pen.760211806

出版商:Society of Plastics Engineers, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractThe kinetic model for irreversible novolac type phenol formaldehyde polymerization and equations governing the molecular weight distribution (MWD) of the polymer formed in homogeneous continuous‐flow stirred tank reactors (HCSTR) have been derived. The set of algebraic equations involves three reaction parametersR1,R2, andR3and have been solved using Brown's algorithm which was found to be more efficient than the Gauss‐Jordon technique of solution. A sensitivity analysis of different reaction parameters has been carried out and the reactivity of the para position was found to be an important factor affecting the MWD. In view of the fact that parametersR1andR2have a negligible effect on MWD, the phenomenon of molecular shielding described by Drummet al.(1) can be neglected. The novolac formation can then be equivalently described by assumingR1= 1 andR2=R3and the kinetic description so obtained is completely based on the experimentally observed different reactivities of ortho and para sites. The results for HCSTR have been compared with those for batch reactors and the former is found to give polymer of lower average molecular weights having higher polydispersity in

ISSN:0032-3888    

DOI:10.1002/pen.760211807

出版商:Society of Plastics Engineers, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractThe fracture toughness of a filled nitrile rubber/phenolic polymeric system was assessed by means of ductile‐to‐brittle transition temperature (DBTT) as measured by the Charpy impact method to search for sampling location dependencies of toughness in structures. This investigation established the relationship between the Charpy DBTT and exposure to selected relative humidity (RH) for the filled polymer from the three lots. Charpy fracture tests of specimens subjected to a low RH environment (15 percent) had higher DBTTs than their counterparts exposed to a high RH condition (70 to 75 percent). Charpy specimens of this material exhibited a 9 to 22°F change in DBTT which depended upon the manufacturer and the conditioning period for a corresponding change of 60 percent RH. The change in DBTT with relative humidity was found to be reversible; initial fracture behavior could be restored to samples from the low RH (15 percent) station by equilibrating at a high RH (75 percent) l

ISSN:0032-3888    

DOI:10.1002/pen.760211808

出版商:Society of Plastics Engineers, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractThis report describes a procedure to stimulate the reaction injection molding process. The analysis considers the conversion that occurs during cavity filling with reactive fluids and the subsequent cure in the mold based on initial conditions derived from the filling analysis. Extensive conversion can occur during cavity filling when highly reactive resins are used. High conversion material with attendant high viscosity can be found in the cavity during filling without flow seizure because the conversion is non‐uniform. The overall cycle time can be decreased by promoting conversion during cavity filling as long as flow seizure is avoided. Temperature and conversion profiles during cure in the mold elucidate thermal runaway and its importance in reaction injection molding. The simulation can be used to explore material and process parameter sensitivity, predict the cycle time and the maximum exotherm temperature, and evaluate moldabilit

ISSN:0032-3888    

DOI:10.1002/pen.760211809

出版商:Society of Plastics Engineers, Inc.    

年代:1981

数据来源: WILEY

ISSN:0032-3888    

DOI:10.1002/pen.760211801

出版商:Society of Plastics Engineers, Inc.    

年代:1981

数据来源: WILEY